The invention relates generally to electrical insulation systems. More particularly, some embodiments of the invention relate to electrical insulation systems including multi-strand, multi-turn conductor winding insulation and ground wall insulation, in a medium or high voltage rotating machine.
With the use of any electrical machines, there is a need to electrically insulate the conductors in the machines. The need for electrical insulation in the machines increases with higher operating voltages. With increasing use of pulse width modulated (PWM) drives, electric machines experience premature electrical failure caused by higher electrical stress on winding insulation, due in part to uneven voltage distribution under high dV/dt conditions. One way to address insulation deficiency is to increase insulation build. However, this can lead to large machine size and poor heat conduction. Thus, a better insulation system that can enable reduction of electrical machine size for high power applications is desired.
Another need within an electrical machine is thermal energy dissipation. Therefore, there is a need for thermally conductive electrical insulators in medium or high voltage electrical machines. Further, insulation systems with higher mechanical strength and thermal stability are sometimes very desirable.
Traditionally, various epoxy resins, mica tapes, or glass fibers were used in electrical insulation systems. However, microvoids may be created during the impregnation or curing of the epoxy resins, leading to poor thermal conduction and partial discharge. Further, the partial discharge resistance of epoxy resins or pure polymer films may be lower than required for certain electrical machines. Mica tapes and glass fibers may not have the mechanical stability required for the robust performance of the electrical machine.
Mica tape made of mica paper with polyester film demonstrated good taping quality and high breakdown strength. However it can be deficient, in terms of long term voltage endurance, due to the poor corona resistance of polyester film. Mica tape made of mica paper with fiberglass is known to have good long term voltage endurance performance, but can have poor taping quality and lower dielectric breakdown strength. The thermal conductivity of mica tape may be increased by adding thermally conductive particulates to the binding resin. This is particularly suitable for resin-rich mica tape, for heat press or autoclave processes, but may not be good for mica tape that is used in vacuum pressure impregnated (VPI) machines, for high power applications.
Therefore, there is a need for a comprehensive approach to the electrical insulation system of medium to high voltage electrical machines, e.g., those that operate in the range of about 4160 V to 15000 V.